Exhalation valve assembly with integrated filter and flow sensor

ABSTRACT

An exhalation valve assembly that controls the pressure of exhaled gas in a ventilation system is described. The exhalation valve assembly includes an actuator module that may be fixed to the ventilation system and a valve module, removable for cleaning or disposal, through which the exhaled gas flows and that controls the pressure and release of the exhaled gas to the environment. Other components may also be incorporated into the assembly including a filter module, a flow meter and a condensate trap.

RELATED APPLICATIONS

This application is related to co-owned U.S. patent application Ser.Nos. 12/628,803; 12/628,905; 12/628,882; and 12/628,856, all filed Dec.1, 2009, the entire disclosures of all of which are hereby incorporatedherein by reference.

INTRODUCTION

Medical ventilators are designed to control the delivery of respiratorygas to a patient to supplement the patient's breathing efforts or tocause the inflation and deflation of a non-breathing patient's lung.Ventilators are often used in conjunction with a dual-limb patientcircuit that conveys respiratory gas to a patient through a first tubereferred to as the inspiratory limb and return exhaled gas from thepatient through a second tube referred to as the expiratory limb.

In order to accurately control the delivery of respiratory gas, pressurein the patient circuit is controlled so that gas is released during anexhalation phase and, typically but not always, flow is completelyblocked during an inhalation phase. However, the ventilator circuit andparticularly the expiratory limb that handles the patient's exhaled gasis a challenging environment. This is true both for the control of thepressure and flow in the expiratory limb, for the monitoring that mustbe performed in order to accurately control the pressure and flow, andfor the capture of any potentially contagious material that may beexhaled by the patient.

SUMMARY

An exhalation valve assembly that controls the pressure of exhaled gasin a ventilation system is described. The exhalation valve assemblyincludes an actuator module that may be fixed to the ventilation systemand a removable valve module through which the exhaled gas flows andthat controls the pressure and release of the exhaled gas to theenvironment. Other components may also be incorporated into the assemblyincluding a filter module, a flow meter and a condensate trap.

In part, this disclosure describes an exhalation valve assembly forcontrolling pressure in a ventilation system. The exhalation valveassembly includes a valve module, an actuator module, a filter moduleand at least one flow sensor. The valve module includes a valve body andattached seal element, in which the valve body defines an inlet portproviding access to a valve chamber and an exhaust port allowing gas toexit the valve chamber. The valve body having a valve seat opposite theattached seal element wherein displacement of the seal element relativeto the valve seat controls gas pressure within the inlet port. Theactuator module is removably connectable to the valve module so that,when attached to the valve module, it is operable to move the diaphragmrelative to the valve seat to control the pressure of gas in the inletport and the release of gas via the exhaust port. The filter moduleincludes a filter body containing filter media and is removablyconnectable to the valve module. The filter module, when attached to thevalve module, filters gas delivered to the exhalation valve assemblyprior to the gas entering the inlet port of the valve module. Thecondensate trap includes a trap body attached to the filter body andreceives the gas delivered to the exhalation valve assembly prior todelivery of the gas to the filter body. The condensate trap holds thegas received in a condensate chamber for a first residence time based onthe condensate chamber's volume and gas flow therethrough and collectsmoisture that condenses from the gas during the first residence time.The flow sensor is contained within a flow sensor chamber in the valvebody monitoring the flow of gas between the inlet port and the valveseat.

This disclosure also describes a respiratory ventilation system thatincludes a pressure delivery system, an inspiratory limb, an expiratorylimb and an exhalation valve assembly comprising a valve module, anactuator module, a filter module and a flow sensor. The valve moduleincludes a valve body and attached seal element, in which the valve bodydefines an inlet port that receives the exhaled gas from the expiratorylimb and directs it to through a valve seat to a valve chamber and anexhaust port allowing exhaled gas to exit the valve chamber. The valveseat is opposite the attached seal element wherein displacement of theseal element relative to the valve seat controls gas pressure within theexpiratory limb. The actuator module is removably connected to the valvemodule and, when attached to the valve module, is operable to move theseal element relative to the valve seat to control the pressure of gasin the inlet port and the release of gas via the exhaust port. Thefilter module comprises a filter body containing filter media and isremovably connectable to the valve module. Wherein the filter module,when attached to the valve module, filters gas delivered to theexhalation valve assembly prior to the gas entering the inlet port ofthe valve module. The flow sensor is contained within a flow sensorchamber in the valve body monitoring the flow of gas between the valveinlet port and the valve seat.

The disclosure further describes a method of controlling pressure in anexpiratory limb of a ventilation system. The method includes receiving apatient's exhaled gas from an expiratory limb through a filter inletport into a filter module comprising a removable filter body thatcontains filter media. The exhaled gas is filtered by allowing apressure differential between the expiratory limb and the atmosphere todrive the gas through the filter. The method also includes passing thefiltered exhaled gas into a removable valve body connected to theventilation system, in which the removable valve body has a valve bodyinlet port, an exhalation port through which gas is released to theenvironment and a surface comprising a seal element. The method furtherincludes displacing a member external to the removable valve body thatinterfaces with the seal element on the removable valve body, therebychanging a distance between the seal element and a valve seat in theremovable valve body and controlling the pressure of the exhaled gas inthe expiratory limb. The flow of gas through the assembly is monitoredwith a flow meter located between the valve inlet port and the valveseat of the removable housing.

These and various other features as well as advantages whichcharacterize the systems and methods described herein will be apparentfrom a reading of the following detailed description and a review of theassociated drawings. Additional features are set forth in thedescription which follows, and in part will be apparent from thedescription, or may be learned by practice of the technology. Thebenefits and features of the technology will be realized and attained bythe structure particularly pointed out in the written description andclaims hereof as well as the appended drawings.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and areintended to provide further explanation of the invention as claimed.

BRIEF DESCRIPTION OF THE DRAWINGS

The following drawing figures, which form a part of this application,are illustrative of described technology and are not meant to limit thescope of the invention as claimed in any manner, which scope shall bebased on the claims appended hereto.

FIG. 1 illustrates an embodiment of a ventilator connected to a humanpatient.

FIG. 2 schematically depicts the exemplary flow and control of gasthrough the system.

FIG. 3 illustrates an embodiment of an exhalation valve assembly havinga removable valve module.

FIG. 4 illustrates another embodiment of an exhalation valve assemblyhaving an exhalation valve module with incorporated pressure and/or flowsensors.

FIG. 5 illustrates yet another embodiment of an exhalation valveassembly having an exhalation valve module with incorporated filter andcondensation trap.

FIG. 6 illustrates a second embodiment of an exhalation valve assemblyhaving an exhalation valve module with incorporated filter andcondensation trap.

FIG. 7 illustrates a locking mechanism that switches between acontagious and non-contagious patient configuration.

FIG. 8 a illustrates the embodiment in a contagious configuration inwhich the contamination control latch is set to a contagious positionand in which the valve module and filter/trap module are shown as aconnected assembly removed from the actuator module which would be fixedto the ventilator housing (not shown).

FIG. 8 b illustrates the same embodiment as FIG. 8 a, but in thenon-contagious configuration in which the filter body is illustrated asbeing separated from the now-latched valve module and actuator moduleassembly.

DETAILED DESCRIPTION

This disclosure describes embodiments of exhalation valve assemblies foruse in ventilators. An exhalation valve assembly controls the pressurein the ventilator patient circuit via releasing exhaled gas from thecircuit. In addition, the designs are described herein that improve theserviceability of the valve assembly, the capture of exhaled liquid andthe filtration of the exhaled gas. In part, this is achieved byproviding a separate actuator module and a removable valve moduledesigned to control the pressure in the ventilator circuit so thatexhaled gas contacts only the removable valve module. Depending on theembodiment, a removable filter/trap module may also be provided thatincludes a filter and condensate trap.

Although the techniques introduced above and discussed in detail belowmay be implemented for a variety of medical devices, the presentdisclosure will discuss the implementation of these techniques in thecontext of a medical ventilator for use in providing ventilation supportto a human patient. The reader will understand that the technologydescribed in the context of a medical ventilator for human patientscould be adapted for use with other systems such as ventilators fornon-human patients and general gas transport systems in whichpotentially contaminated gas must be pressure-controlled and filteredbefore release to the atmosphere.

Medical ventilators are used to provide a breathing gas to a patient whomay otherwise be unable to breathe sufficiently. In modern medicalfacilities, pressurized air and oxygen sources are often available fromwall outlets. Accordingly, ventilators may provide pressure regulatingvalves (or regulators) connected to centralized sources of pressurizedair and pressurized oxygen. The regulating valves function to regulateflow so that respiratory gas having a desired concentration of oxygen issupplied to the patient at desired pressures and rates. Ventilatorscapable of operating independently of external sources of pressurizedair are also available.

FIG. 1 illustrates an embodiment of a ventilator 20 connected to a humanpatient 24. Ventilator 20 includes a pneumatic system 22 (also referredto as a pressure generating system 22) for circulating breathing gasesto and from patient 24 via the ventilation tubing system 26, whichcouples the patient to the pneumatic system via physical patientinterface 28 and ventilator circuit 30. Ventilator circuit 30 could be atwo-limb or one-limb circuit for carrying gas to and from the patient.In a two-limb embodiment as shown, a wye fitting 36 may be provided asshown to couple the patient interface 28 to the inspiratory limb 32 andthe expiratory limb 34 of the circuit 30.

The present systems and methods have proved particularly advantageous ininvasive settings, such as with endotracheal tubes. However, the presentdescription contemplates that the patient interface may be invasive ornon-invasive, and of any configuration suitable for communicating a flowof breathing gas from the patient circuit to an airway of the patient.Examples of suitable patient interface devices include a nasal mask,nasal/oral mask (which is shown in FIG. 1), nasal prong, full-face mask,tracheal tube, endotracheal tube, nasal pillow, etc.

Pneumatic system 22 may be configured in a variety of ways. In thepresent example, system 22 includes an exhalation valve assembly 40coupled with an expiratory limb 34 and an inspiratory module 42 coupledwith an inspiratory limb 32. Compressor 44 or another source or sourcesof pressurized gas (e.g., pressured air and/or oxygen controlled throughthe use of one or more gas regulators) is coupled with inspiratorymodule 42 to provide a source of pressurized breathing gas forventilatory support via inspiratory limb 32.

The pneumatic system may include a variety of other components,including sources for pressurized air and/or oxygen, mixing modules,valves, sensors, tubing, accumulators, air filters, etc. Controller 50is operatively coupled with pneumatic system 22, signal measurement andacquisition systems, and an operator interface 52 may be provided toenable an operator to interact with the ventilator (e.g., changeventilator settings, select operational modes, view monitoredparameters, etc.). Controller 50 may include memory 54, one or moreprocessors 56, storage 58, and/or other components of the type commonlyfound in command and control computing devices.

The memory 54 is computer-readable storage media that stores softwarethat is executed by the processor 56 and which controls the operation ofthe ventilator 20. In an embodiment, the memory 54 comprises one or moresolid-state storage devices such as flash memory chips. In analternative embodiment, the memory 54 may be mass storage connected tothe processor 56 through a mass storage controller (not shown) and acommunications bus (not shown). Although the description ofcomputer-readable media contained herein refers to a solid-statestorage, it should be appreciated by those skilled in the art thatcomputer-readable storage media can be any available media that can beaccessed by the processor 56. Computer-readable storage media includesvolatile and non-volatile, removable and non-removable media implementedin any method or technology for storage of information such ascomputer-readable instructions, data structures, program modules orother data. Computer-readable storage media includes, but is not limitedto, RAM, ROM, EPROM, EEPROM, flash memory or other solid state memorytechnology, CD-ROM, DVD, or other optical storage, magnetic cassettes,magnetic tape, magnetic disk storage or other magnetic storage devices,or any other medium which can be used to store the desired informationand which can be accessed by the processor 56.

As described in more detail below, controller 50 issues commands topneumatic system 22 in order to control the breathing assistanceprovided to the patient by the ventilator. The specific commands may bebased on inputs received from patient 24, pneumatic system 22 andsensors, operator interface 52 and/or other components of theventilator. In the depicted example, operator interface includes adisplay 59 that may be touch-sensitive, enabling the display to serveboth as an input user interface and an output device.

FIG. 2 schematically depicts the exemplary flow and control of gasthrough the system. As shown, controller 50 issues control commands todrive the pressure delivery system 22 (which in the embodiment showncollectively refers to the inspiratory module 42 and any equipmentnecessary to receive gas from the respiratory gas source 44 such asmixing manifolds, accumulators, regulators, etc.) and thereby deliverbreathing gas to the patient 24 via the patient circuit. Exhaled gas isremoved from the patient 24 via the expiratory limb of the patientcircuit and discharged to the ambient environment through the exhalationvalve assembly 40. In the embodiment shown the flow of gas through thesystem and the pressure of gas within the system is controlled by thecontroller's management of the delivery of gas through the inspiratorymodule 42 and the pressure in the circuit via the controller'smanagement of the release of gas by the exhalation valve module 50.

FIG. 3 illustrates an embodiment of an exhalation valve assembly. Theexhalation valve assembly 300 is illustrated in a sectional, explodedview to conceptually show the different components of the assembly andhow they operate relative to each other. The exhalation valve assembly300 shown can be considered as having two distinct elements: an actuatormodule 302 that is a fixed part of the ventilator (not shown) and aremovable valve module 304. The valve module 304 receives exhaled gasfrom a patient through an inlet port 306 and discharges it to theambient atmosphere via an exhaust port 308. As described below, theactuator module 302 physically interfaces with the valve module 304 tocontrol the pressure of gas in the inlet port 306 of the valve module304 by changing the position of a valve seal 332 in the valve module 304with respect to a valve seat 326. By controlling the pressure in theinlet port 306 the actuator module 302 also affects the flow of gasthrough the valve module 304. The designs are such that the removablevalve module 304 contains all components that are exposed to the exhaledgas from the patient. In this way, cleaning the exhalation assemblyrequires only replacement or cleaning of the used exhalation valvemodule 304.

In the embodiment shown, the actuator module 302 is incorporated intothe ventilator and includes a drive element 314 that displaces a member316, such as a poppet or shaft. As shown, the drive element 314 is alinear motor, such as a voice coil motor, that drives a poppet 316.Alternative drive elements 314 include piloted pressure chambers,stepper motors, solenoids or any device capable of displacing a memberor surface or applying a force on a member or surface. Although the termdisplacement is primarily used herein, one of skill in the art willrecognize that the pressure is regulated primarily from the applicationof force to the seal element. The term displacement is used as shorthandfor this process. Likewise, the poppet 316 may be replaced by a shaft,pin, or surface that can be displaced from the actuator module 302.

The actuator module 302 also includes an attachment portion or mechanism(not shown) that interfaces with the valve module 304 allowing the valvemodule 304 to be removably attached to the actuator module 302. Theattachment portion includes one or more connector elements that matewith complementary elements on the valve module 304. Examples ofconnector elements include latches, levers, clasps, spring loadedelements, threads for screw mounting, or snaps and any suitableattachment technique, now known or later developed, may be used. Theattachment portion allows the valve module 304 to be installed in a waythat the poppet 316 is positioned adjacent to a moveable seal 332 on thevalve module 304 (illustrated in FIG. 3 by poppet 316 in dashed lines).The attachment portion may also be designed to prevent the valve module304 from being connected to the actuator module 302 in any non-operableconfiguration.

In the embodiment shown, the valve module 304 includes a valve body 322and a valve seal with integrated diaphragm (the valve seal withintegrated diaphragm will be referred to collectively as the sealelement 330 and will be discussed in greater detail below).

The valve body 322 may be a unitary body of any suitable material suchas plastic, aluminum, stainless steel, etc., however, because undercertain conditions the valve module 304 may be treated as a disposablecomponent, expensive materials are not preferred. In the embodimentillustrated in FIG. 3, the valve body 322 partially defines an interiorvolume referred to generally as the valve chamber 324. The valve body322 also includes an inlet port 306 and an exhaust port 308, both ofwhich provide access to the valve chamber 324. In the embodiment shown,the inlet port 306 provides access to the valve chamber 324 through thevalve seat 326. In an alternative embodiment (not shown), the valve seat326 is located at the exhaust port 308 instead of the inlet port 306.

The valve body 322 also provides access to the valve chamber 324 througha seal/diaphragm orifice 328. The edge of the seal/diaphragm orifice 328may be provided with one or more retainers such as lips, ridges or ribsso that the seal element 330 can be removably attached. When attached,the seal element 330 and the valve body 322 form a substantiallyairtight seal so that the inlet port 306 and the exhaust port 308 arethe only routes for gas to enter the valve chamber 324. In analternative embodiment, the seal element 330 may be irremovably attachedto the valve body 322, for example the two components may be bondedtogether by adhesive or in some other manner.

The seal element 330, as mentioned above, comprises a valve seal 332portion and integral flexible diaphragm 334 portion. In an embodiment,the seal element 330 is a unitary construction of molded, flexiblematerial such as silicon rubber. Preferably, the material is flexibleand resists wear and degradation. Although silicon rubber is preferreddue to its resistance to degradation over time and other properties,less desirable materials such as viton rubber, elastomers or similar maybe used. Alternatively, the seal element 330 may be made from a flexiblediaphragm made out of a first material bonded to a valve seal 332 madefrom a second material having different properties. In yet anotherembodiment, the seal 332 or the diaphragm 334 may be coated on one orboth sides with compounds that reduce the gas transport through the sealelement 330 or improve the performance of the valve seal 332, such as byimproving its interface with the valve seat 326.

When molded as a unitary construction, the diaphragm 334 and the valveseal 332 portions of the seal element 330 may be provided with differentshapes, thicknesses or surfaces in order to improve the performance ofthe seal element 330. For example, the diaphragm 334 may be shaped toimprove the flexibility of the diaphragm 334 by providing curvedsections as shown. Likewise, the seal 332 may be molded with arelatively thicker cross section having a surface shaped to be thecompliment of the valve seat 326. Any suitable design for the sealelement 330 may be used as long as the seal element 330 can beeffectively displaced by the actuator module 302 to control the pressurein the inlet port 306.

In a ventilator embodiment, the inlet port 306 is attached to andreceived exhaled gas from the expiratory limb of the ventilation system.As may be appreciated from the discussion above, the valve module 304creates a flow path through the inlet port 306 into the valve chamber324 and out through the exhaust valve 308 to the atmosphere. The flowpath goes through the valve seat 326 opposed by the valve seal 332. Therelative position of the poppet 316 to the valve seat 326 is changed inorder to control the pressure in the inlet port 306. Depending on theembodiment, the valve seat 326 may be located at the entrance of theinlet valve (as shown) into the valve chamber 324 or at some otherlocation along the flow path. Due to the separation of the actuatormodule 302 from contact with exhaled gas by the seal element 330, anycontamination due to contact with exhaled gas is limited to the internalsurfaces of the valve module 306.

FIG. 4 illustrates an embodiment of an exhalation valve assembly with anintegrated pressure and/or flow sensing capability. Again, theexhalation valve assembly 400 shown can be considered as having twodistinct elements, an actuator module 402 and a removable valve module404. In the embodiment shown, in addition to controlling the pressure ofgas in the inlet port of the valve module 404 and isolating exhaled gasin the removable valve module 404, the exhalation valve assembly 400includes one or more sensors 450, 452, 454, 456 that report data to theventilator. With the exception of the sensors described below, theactuator module 402 and valve module 404 are as described above withreference to FIG. 3.

FIG. 4 illustrates several different flow and pressure sensorconfigurations which could be implemented separately and independentlyor in any combination. The data from any or all of these configurationscould be used by ventilation system in the delivery of respiratory gasto the patient. For example, one or more of the sensors described abovecould be used to provide the expiratory limb flow or pressure datanecessary to delivery respiratory to the patient.

A first sensor configuration is a flow sensor 450 in the form of adifferential pressure sensor that comprises a pressure sensor 450 sconnected to two pressure taps 450 a and 450 b providing access todifferent points in the flow path through the valve module 404. One tap450 a provides access to the flow path on the inlet side of the valveseat 426, illustrated as a pressure tap into the valve module inlet port406. The other tap 450 b provides access to the flow path on the exhaustside of the valve seat 426, illustrated as a pressure tap into the valvechamber 424 although it could also be located in the exhaust port 408.Depending on the exact location of the valve seat 426 relative to theinlet and exhaust ports, either of the taps could be located to provideaccess to the valve chamber 424. As is known in the art, flow can bedetermined by measuring the differential pressure across a known flowrestriction under known conditions of temperature and gascharacteristics. In this configuration, the restriction is provided bythe orifice between the valve seat 426 and the seal 432. Although thisorifice is variable, it can be determined at any time through the use ofa position sensor 420 in the actuator module 402. In this configuration,the position of the poppet 416 is correlated with an orifice size sothat if the position is known, the resulting orifice size is known. Sucha correlation may be predetermined by the manufacturer or periodicallydetermined calibrated under conditions of known flow, such as during aventilator startup routine. Other information necessary to thedetermination of flow using the flow sensor 450 (e.g., temperature, gasdensity, etc.) may be obtained in real time from the ventilationsystem's monitoring of the patient circuit or may be assumed.

In another sensor configuration a flow sensor 452 is provided in theform of a differential pressure sensor that comprises a pressure sensor452 s connected to a pressure tap 452 a providing access to the flowpath on the inlet side of the valve seat 426, illustrated as a pressuretap into the inlet port 406. Instead of providing a second tap into thevalve module 404, the pressure sensor 452 s uses the ambient atmosphericpressure obtained from any location near the ventilator. In thisconfiguration, one simple embodiment is to provide a tap 452 b to theatmosphere at some point near the pressure sensor 450 s. In thisconfiguration like the previous one described, the restriction isprovided by the orifice between the valve seat 426 and the seal 432 andotherwise operates in a similar fashion.

In yet another sensor configuration a flow sensor 454 is provided in theform of a differential pressure sensor that comprises a pressure sensor454 s connected to two pressure taps 454 a and 454 b providing access toeither side of a fixed restriction 454 r in the flow path. The pressuretaps 454 a, 454 b and flow restriction 454 r may be located anywhere inthe flow path in the valve module 404. FIG. 4 illustrates the pressuretaps 454 a, 454 b and flow restriction 454 r as being located in theexhaust port. The flow sensor 454 (that is pressure taps on either sideof a known flow restriction) corresponds to a standard design and iswell known in the art.

In yet another configuration, a flow meter such as a hot wire anemometerflow meter 456 is provided at some location in the flow path through thevalve module 404. Although any flow meter may be used, hot-wireanemometers flow meters have the advantages of being small and having nomoving parts. Hot wire anemometer-based flow meters are known in theart, and such flow meters may measure flow based on the cooling of aheated wire or based on the current required to maintain a wire at afixed temperature when the wire is exposed to the flow of gas. In theembodiment shown, the flow meter 456 is located in the inlet port 406 atthe base of the valve seat 426. Although a hot wire anemometer-basedflow meter is described, any suitable flow meter now known or laterdeveloped may be used.

Any combination of the configurations described above may also be used.For example, in a preferred embodiment a pressure sensor, such as thepressure sensor 452 s connected to a pressure tap 452 a providing accessto the flow path on the inlet side of the valve seat 426 and which thepressure sensor 452 s uses the ambient atmospheric pressure obtainedfrom any location near the ventilator, and a flow meter 456 are bothprovided. Using the information concerning the known distance betweenthe valve seat and the seal element, the pressure sensor 452 s data canbe used to calculate a second estimate of the flow of gas through thevalve module at any given time. Such a calculation may involveperforming actual mathematical computations or may simply involvecorrelating a measured pressure drop and an indicator of the distancebetween the valve seat and the seal element using a predeterminedlook-up table describing a known relationship between the flow,differential pressure and seal element location. The two flow values,that measured directly using the flow meter 456 and that calculated fromthe pressure differential, can then be compared in order to makeassessments as to the different aspects of the ventilation system and toprovide better control of the gas delivery to the patient. For example,the ventilation system may perform one or more actions related to thedelivery of gas to the patient based on the comparison of the two flowvalues. Such actions may include transmitting an alarm or notificationregarding the performance of either the flow meter 456 or the pressuresensor 452 s; using a flow value derived from two flow values, e.g., anaverage of the two, to change the pressure or flow of gas beingdelivered to the patient.

FIGS. 5-6 illustrate alternate embodiments of an exhalation valveassembly with a valve module and a filter and condensation trap. For thesake of discussion the assembly shown in FIG. 5 can be considered tohave three elements: an actuator module 502 and a valve module 504 suchas those described above; and a filter/trap module 560. The filter/trapmodule 560 introduces a filter 562 and condensate trap 564 into the flowpath prior to exhaled gas entering the valve module 504. The filter/trapmodule 560 connects to valve module 504 and may be independentlyremovable from the valve module 504 in order to allow for easy disposalof the enclosed filter media and any condensation captured in the trap.As discussed in greater detail below with reference to FIG. 7, thefilter/trap module 560 may also be removed from the ventilator byremoving the valve module 504 with the filter/trap module 560 attached,thus removing all components of the exhalation assembly that were incontact with exhaled gas.

FIG. 5 illustrates an embodiment of an exhalation valve assembly with avalve module and a filter and condensation trap in which the actuatormodule 502 and the valve module 504 are as described above withreference to either FIG. 3 or 4. The valve module 504 includes anattachment surface or mechanism (not shown) allowing the filter/trapmodule 560 to be attached. As described above, the attachment surfacemay incorporate any suitable attachment means for attaching the twomodules. For example, any attachment surface may incorporate a seal,such as an O-ring or other sealing device 561, in order to provide agreater level of airtight fit when components are attached.

In the embodiment shown, the filter/trap module 560 can be considered astwo distinct components, a filter component 572 that includes a filterbody 574 enclosing a volume referred to as the filter chamber 568 thatcontains the filter 562; and a condensate trap component 564 thatconsists primarily of a trap body 576 formed to act as a condensatetrap. The two components 572, 564 may be a unitary body or may be twoseparate bodies that are removably connected (e.g., the trap 564 can beunscrewed or unclipped from the filter body 574) as shown in theexploded view in FIG. 5. As described above, the bodies of the twocomponents may be made of any suitable material. In an embodiment,transparent plastic is used so that the level of condensate in the trap564 and the condition of the filter 562 can be visually inspected.Alternatively one or more transparent windows in an opaque material maybe provided for visual inspection. As discussed in greater detail below,it is beneficial to independently control the temperature of the twocomponents and the selection of body materials may be made to facilitateor inhibit heat transfer depending on the embodiment.

The filter/trap module 560 alters the flow path of the exhaled gas priorto entering the valve module 504. Exhaled gas is received from theexpiratory limb of the ventilation system and enters the filter/trapmodule 560 at the trap inlet port 566. After a residence time in thecondensate trap 564, exhaled gas flows into the filter chamber 568 andthrough the filter 562 (diffusion through the filter being illustratedby wavy airflow lines). Filtered gas then flows through the filterexhaust port 570 into the valve module inlet port 506.

Turning now to the condensate trap 564, in an embodiment the condensatetrap 564 consists essentially of the trap body 576 enclosing a volumereferred to as the condensate chamber. In an embodiment, the volume ofthe condensate chamber may be selected in order to provide a specificresidence time under average flow conditions, noting that the residencetime of the condensate chamber is equivalent to its volume divided bythe flow rate of gas. The residence time may be selected based on theheat transfer characteristics of the materials and configuration of themodules in order to provide sufficient time for moisture in the exhaledgas to condense out of the gas stream. The trap body 576 also includes atrap inlet port 566 to which an expiratory limb (not shown) can beattached to receive exhaled gas and an attachment portion for attachingthe trap body 576 to the filter body 574. In the embodiment shown, thetrap body 576 is roughly cup-shaped with the attachment portion at theopening of the cup. The trap body 576 attaches to the filter body 574 sothat the opening of the cup-shaped body is covered by the filter body574 and encloses the condensate chamber.

In an embodiment, the condensate trap 564 may be provided with amanifold, diffuser, fin or other passive flow control element thatdirects the flow of the exhaled gas entering the condensation chamber.One purpose of this is to promote the cooling of the exhaled gas tofacilitate condensation of any moisture exhaled by the patient. Improvedcooling results in relatively more condensate getting caught in the trap564 which improves the performance of the filter 562 and the otherdownstream components.

For example, in an embodiment the trap inlet port 566 may be located andoriented in an off-center configuration so that gas flow enters flowingin a direction that is tangential against an interior wall of thecondensate trap body 576, thereby creating a flow along the interiorsurface of the trap body 576 without redirecting the incoming flow usinga flow control element. Alternatively, the inlet trap inlet port 566could be configured so that gas flow enters the condensate chamber andis redirected by fin or other flow control element to travel along awall of the condensate chamber. Both embodiments have the effect ofcreating a vortex flow in the condensate chamber and along interiorwall's surface, thereby increasing the heat transfer between the wallsof the trap body and the incoming gas. However, use of flow controlelement may increase the resistance of the assembly 500 to flow, whichmay not be preferred. Additional passive flow control elements such asfins that direct the flow in a spiral pattern around the condensationchamber before the flow exits into the filter body 574 may be provided.

Additional modifications may be made to facilitate the cooling of thecondensate trap 564. For example, in the embodiment shown the condensatetrap 564 when attached to the ventilator is exposed to the ambientatmosphere. As most medical environments are maintained at a relativelycool temperature, this serves to cool the condensate trap 564. Inanother embodiment, a circulation fan on the ventilator may be providedthat directs a flow of cool air onto the condensate trap 564. In yetanother embodiment, a cooling element such as a chilled surface may beprovided on the ventilator that contacts the condensate trap 564 whenthe trap is installed. Other methods for cooling the condensate chamberwill be immediately suggested to one skilled in the art and any suchmethod may be employed.

In an embodiment the condensate trap 564 may be provided with a drainfor the removal of any condensate that may be collected. Alternatively,removal of condensate may be accomplished by removing the trap body 576and either replacing it with a new body 576 or emptying the condensatefrom it before reattaching it. In yet another embodiment, it may bedesirable to prevent removal of the condensate during ventilation, inwhich case the trap body 576 may be fixed or integral with the filterbody 574 so that the only way to remove the condensate is to remove andreplace the filter/trap module as a unit. In yet another embodiment, thecondensate may be drained from the filter body 574 through a drain port(not shown).

The filter chamber 568 contains the filter 562 which effectively dividesthe chamber 568 into two volumes: a first volume 580 that receives theunfiltered gas from the condensate trap and a second volume 582 thatcollects the filtered gas. In the embodiment shown, a hollow cylindricalfilter 562 is illustrated and unfiltered gas is filtered by passing thegas from the exterior 580 of the filter chamber into the annulus 582 atthe center of the filter 562. The top and bottom of the cylindricalfilter 562 are sealed to the interior surface of the filter chamber 568to prevent unfiltered gas from getting into the annulus 582. Otherfilter configurations are also possible and any suitable filter shape orconfiguration could be used so long as it is contained with a filterbody 574 and filters the gas leaving condensate trap 564 prior todelivering it to the valve inlet port 506.

The filter component 572 includes a filter inlet port 578 provided inthe filter body so that when the filter body 574 and condensate trapbody 576 are attached, cooled gas can enter the filter component fromthe condensation chamber. In the embodiment shown, the filter inlet port578 is located within the portion of the filter body that covers theopening of the condensate trap body to enclose the condensate chamber.Other configurations are possible.

The filter inlet port 578 directs the exhaled gas from the condensatechamber to the first volume 580 in the filter chamber 568. This may befacilitated by the use of a manifold or other passive flow distributionmechanism in order to evenly distribute the gas to be filtered along thesurface of the filter 562. After gas has passed through the filter 562it enters the second volume 582 of the filter chamber and then exits viathe filter exhaust port 570 into the valve module 504.

In an embodiment, the filter body 574 is detachable from both the valvemodule 504 and the condensate trap 564 and the body 574 is provided withthe necessary attachment mechanisms to facilitate this. Again, anyspecific attachment mechanism or technique may be utilized.

When attached to the valve module 502, the filter chamber 568 is fullyenclosed by the valve body 522 and the filter body 574 such that theonly flow paths into or out of the filter body 574 are the filter inletport and the filter exhaust port. In the embodiment shown in FIG. 5, thefilter body 574 is substantially cup-shaped in which the bottom of thecup is shaped to sealingly engage one end of the tubular filter 562. Theother end of the filter 562 is adapted to engage an exterior surface ofthe valve body 522 such that detachment of the filter body 574 from thevalve body 522 allows the filter 562 to be accessed andremoved/replaced. In this embodiment, the filter exhaust port may beformed by the annulus of the filter 562 which is exposed to the valveinlet port 506. Depending on the embodiment, the valve inlet port 506may be provided with a protrubing nipple or tube (not shown) for guidingthe attachment of the filter body 574 to the valve body 522 andproviding a better seal between the valve body and the filter. The valveinlet port 506 may also be designed to provide flow shaping andpre-conditioning, such as to prepare the flow for measurement.

In an alternative embodiment, a removable cap (not shown) may beprovided that attaches to the filter body 574 in order to enclose thefilter 562 into the filter chamber 568. The cap may be provided with ahole or aperture as the filter exhaust port that when installed ispositioned on the valve inlet port.

It may be preferred to maintain the filter chamber 568 at a temperaturegreater than that of the condensate trap to inhibit any furthercondensation within the exhalation assembly 500. In an embodiment thefilter component 572 may be provided with active heating or passiveinsulation. For example, in an embodiment a heating element may belocated in or near the filter body. In yet another embodiment, thefilter body and ventilator housing may be designed to create asubstantially enclosed volume of insulating air around the filter bodyor the portion of the filter body containing the filter chamber. Toeffect this, the filter body 574 may be provided with a partialsecondary wall or integrated cover that complements the shape of theventilator housing around the filter body when it is installed so that asubstantially trapped air space is created around the filter chamber(See FIGS. 8-9 for an illustration of an embodiment of a cover).Alternatively, a movable cover could be provided on the ventilatorhousing that encloses a chamber in the ventilator housing within whichthe filter body resides when installed. Such designs need not beairtight to serve to create an insulating layer of air around the wallsof the filter chamber 568 that is relatively unaffected by the movementambient air outside of the cover and ventilator housing.

In yet another embodiment, such a trapped air space around the filterbody could be actively heated, such as by passing waste heat from theelectronics in the ventilator through the insulating volume or to a heatsink exposed to the insulating volume or by blowing heated air into thetrapped air space. Other ways of heating the filter chamber will beimmediately suggested to one of skill in the art and any such heatingmethods may be used. It should be observed that because of the verticalconfiguration of the exhalation assembly with the condensate trap at thebottom, adding heat (or passively preventing heat from being released tothe ambient atmosphere) serves to reduce any condensation in the modulesabove the condensate trap without interfering with the operation of thecondensate trap.

In an embodiment (not shown), one or more sensors or pressure taps maybe incorporated into or near the filter/trap module 560. For example,pressure taps as described in FIG. 4 located on the inlet side of thevalve seat 526 can be located within the flow

In the embodiment shown, the modules are vertically oriented with theactuator module 502 on top, the valve module 504 below the actuatormodule 502 and the filter component 572 below the valve module and thecondensate trap component 564 below that. This orientation isefficacious for several reasons. One reason is that the seal element 530in the valve module 504 can act as a check valve in cases where there isa sudden drop in the expiratory limb pressure. Another reason is thatthe condensate will naturally pool in the trap body due to gravity. Yetanother reason is that since heat rises, maintaining the condensate trap564 as the lowest component allows for a beneficial heat profile throughthe exhalation valve assembly 500.

FIG. 6 illustrates yet another embodiment of an exhalation valveassembly in which the valve seat is a component of the filter/trapmodule rather than being built into the valve module. In the embodimentshown the actuator module 602, the valve module 604 and the filter/trapmodule 660 are substantially as described above with the exception ofthe valve seat 626. Rather than having the valve seat 626 as a componentof the valve module 604, the valve seat is built into a top portion ofthe filter/trap module 660 that when attached it places the valve seat626 in its position opposite the seal element 630. In this embodiment,the valve body 622 may be provided with a floor having an inlet port 606through which the valve seat 626 penetrates when the filter/trap module660 is installed. Alternatively, the valve body 622 could besubstantially open so that when installed the surface of the filter/trapmodule 660 around the valve seat 626 forms one of the walls defining thevalve chamber 624 as shown.

In the embodiment shown in FIG. 6, the valve module 604 is illustratedas having an outlet port 608 in a hood configuration. The outlet port608 directs the flow the generally downward into a second condensatetrap 609 attached below the outlet port 608 to catch any secondarycondensate that may occur when the exhaust gas exiting the valve module604 is cooled to the ambient temperature.

In either embodiment, with relation to monitoring devices, thefilter/trap module 660 may be modified as described above to include oneor more pressure taps or flow sensors such as hot wire sensors. Forexample, a hot wire flow sensor could be provided between the valve seat626 and the top of the filter 662 such as being built into the top ofthe filter/trap module 660.

In the embodiment of FIG. 6, if the entire filter body is not beconsidered disposable, then access may be effected to the filter 662 byproviding a filter body 674 that can be taken apart. One possible designis providing a removable top (not shown) to the filter body 674 thatincludes the valve seat 626 and that when separated from the rest of thefilter body 674 allows the filter 662 to be removed. Such a removabletop may further be provided with the sensor elements, if any, allowingthe expensive monitoring components to be cleaned and placed back intoservice easily by simply sanitizing the removable top.

The above describes but only a few possible designs of a valve seatintegrated into a filter module. Other methods of mechanicallyincorporating the valve seat into the filter or combined filter and trapmodule rather than the valve module are possible and any such design maybe used.

FIG. 7 illustrates an embodiment of a contamination control switch foruse with an exhalation valve assembly. For the purposes of illustratingthe latch 790, an exhalation valve assembly 700 corresponding to thatshown in FIG. 5 illustrated. That is, the exhalation valve assemblyincludes three main components an actuator module 702 fixed to theventilator, a valve module 704 and a filter/trap module 760.

One purpose of the contamination control latch 790 is to prevent reuseof and ensure the cleaning or disposal of the valve module 704 andfilter/trap module 760 after they has been used with a patientconsidered to be contagious by the treating health professionals. Thecontamination control latch 790 is illustrated conceptually in FIG. 7 asa two position latch attached to the valve body 774 that selectivelyengages either the actuator module 702 or the filter/trap module 760.

In a first, non-contagious patient position 792, the contaminationcontrol latch 790 fixes the valve module 704 to the actuator module 702so that the filter/trap module 760 can be freely removed. This preventsthe accidental removal of the valve module 704 and the filter/trapmodule 760 as a unit from the ventilator.

In a second, contagious patient position 794, the contamination controllatch 790 fixes the valve module 704 to the filter/trap module 760 sothat the filter/trap module 760 can not be removed from the ventilatorwithout either removing the valve module 704 or changing the latchposition 790. This requires the removal of the valve module 704 and thefilter/trap module 760 as a unit through the removal of the valve module704 from the actuator module 702.

In practice, the contamination control latch 790 may be effected by anyone of a number of different designs. For example, a sliding member maybe provided on the valve module 704 that has two positions in which eachposition engages complimentary tabs or openings on one or the other ofthe actuator module 702 and the filter/trap module 760. Fasteners,clamps and locking devices are well known in the art and any suitablemechanism may be used herein. Although a single latch mechanism ispreferred, multiple independent mechanisms such as sliding members,claps, or knobs may also be used.

In an embodiment of the contamination control latch 790 a visualindicator is provided to indicate to the operator which position, thenon-contagious patient position 792 or contagious patient position 794,the assembly 700 is currently in. This may be accomplished in manydifferent ways depending on the particular design selected to performthe function of the contamination control latch 790. For example, if asliding member is used as described above, when in the contagiouspatient position 794 a visual indicia (e.g., text such as “ContagiousPatient” or a biohazard symbol on a yellow field) may be displayed whichis covered by the member when in the non-contagious patient position792.

Variations and other features associated with the contamination controllatch 790 may be provided. For example, in another embodiment the latch790 may be provided with a third position 796, which allows the allcomponents of the assembly 700 to be freely installed or removed. In yetanother embodiment, a mechanical or electrical mechanism may be providedto ensure that a position selection is consciously made by the operator.For example, a prompt during filter change or new patient setupoperation may be presented on the operator via the ventilator's user'sinterface requiring the operator to indicate that the latch 790 has beenplaced in the proper position prior to the delivery of ventilation.Alternatively, the mechanism may be designed such that the components ofthe exhalation valve assembly 700 may not be completely installed untila latch 790 position is selected. Other methods and designs related toensuring that a latch position 792, 794 is selected may also be used.

In an embodiment, the latch 790 can set to the appropriate configuration792, 794 at any time after it has been installed on the ventilator. Thisallows the operator to set the latch position after the initiation ofventilation and the status of the patient has been confirmed. Usually,the ventilator is used in a ward setting and the filter/trap modules arecleaned or disposed of in some remoter service area. The latch 790system described herein provides several benefits in that it not onlyprevents potentially contaminated parts from being retained on theventilator it also provides a visual indicator to service personnelremote from the ward of the status of the patient that was associatedwith the component they are handling. Thus, the latch 790 ensures thatthe filter/trap module comes apart in a way that is appropriate to thecircumstances and alerts the service personnel of the condition of thepatient associated with the module.

FIGS. 8 a-8 b illustrate an embodiment of an exhalation valve assembly800 for controlling pressure in a ventilation system. FIG. 8 aillustrates the embodiment in a contagious configuration in which thecontamination control latch 890 is set to a contagious position 892 andin which the valve module 804 and filter/trap module 860 are shown as aconnected assembly removed from the actuator module 802 which would befixed to the ventilator housing (not shown). FIG. 8 a illustrates theactuator module 802 and poppet 816. The filter/trap module 860 isillustrated as latched to the valve module 804.

In the embodiment a cover 898 is illustrated as a built in component ofthe filter body that, in conjunction with the shape of the ventilatorhousing, creates an insulating space around the portion of the filterbody 874 defining the filter chamber. In addition to the cover integralto the filter body 874, a second hinged cover 899 is illustratedattached to the ventilator housing 895. The second hinged cover 899opens to reveal the location within the ventilator housing 895 intowhich the valve module 804 is installed. Both covers are provided withan opening complementary to the outlet port 808 of the valve module 804,which is most clearly illustrated by FIG. 8 b.

The condensate trap 864 is illustrated connected to the filter body 874.The seal element 830 is illustrated including a separate seal portion inthe center of the seal element and diaphragm that flexibly connects theseal portion to the valve body.

FIG. 8 b illustrates the same embodiment as FIG. 8 a, but with thecontamination control latch 894 in the non-contagious 894 configurationin which the filter body 874 is illustrated as being separated from thenow-connected valve module 804 and actuator module 802 assembly.

It will be clear that the systems and methods described herein are welladapted to attain the ends and advantages mentioned as well as thoseinherent therein. Those skilled in the art will recognize that themethods and systems within this specification may be implemented in manymanners and as such is not to be limited by the foregoing exemplifiedembodiments and examples. For example, the operations and steps of theembodiments of methods described herein may be combined or the sequenceof the operations may be changed while still achieving the goals of thetechnology. In addition, specific functions and/or actions may also beallocated in such as a way as to be performed by a different module ormethod step without deviating from the overall disclosure. In otherwords, functional elements being performed by a single or multiplecomponents, in various combinations of hardware and software, andindividual functions can be distributed among software applications. Inthis regard, any number of the features of the different embodimentsdescribed herein may be combined into one single embodiment andalternate embodiments having fewer than or more than all of the featuresherein described are possible.

While various embodiments have been described for purposes of thisdisclosure, various changes and modifications may be made which are wellwithin the scope of the present invention. Numerous other changes may bemade which will readily suggest themselves to those skilled in the artand which are encompassed in the spirit of the disclosure and as definedin the appended claims.

Unless otherwise indicated, all numbers expressing quantities,properties, reaction conditions, and so forth used in the specificationand claims are to be understood as being modified in all instances bythe term “about.” Accordingly, unless indicated to the contrary, thenumerical parameters set forth in the following specification andattached claims are approximations that may vary depending upon thedesired properties sought to be obtained by the present invention.

What is claimed is:
 1. An exhalation valve assembly for controllingpressure in a ventilation system comprising: a valve module including avalve body and attached seal element, the valve body defining an inletport providing access to a valve chamber and an exhaust port allowinggas to exit the valve chamber, the inlet port and exhaust port being theonly routes for gas to enter the valve chamber, the valve body having avalve seat opposite the attached seal element wherein displacement ofthe seal element relative to the valve seat controls gas pressure withinthe inlet port; an actuator module removably connectable to the valvemodule that, when attached to the valve module, is operable to move adiaphragm relative to the valve seat to control the pressure of gas inthe inlet port and the release of gas via the exhaust port; a filtermodule comprising a filter body containing filter media and wherein thefilter module is removably and directly connectable to the valve module,wherein the filter module, when attached to the valve module, filtersgas delivered to the exhalation valve assembly prior to the gas enteringthe inlet port of the valve module; a condensate trap including a trapbody attached to the filter body, the condensate trap receiving the gasdelivered to the exhalation valve assembly prior to delivery of the gasto the filter body, wherein the condensate trap holds the gas receivedin a condensate chamber for a first residence time based on thecondensate chamber's volume and gas flow therethrough and collectsmoisture that condenses from the gas during the first residence time;and a flow sensor contained within the valve body monitoring the flow ofgas between the inlet port and the valve seat.
 2. The exhalation valveassembly of claim 1, wherein a portion of the valve body is moveable toprovide access to the flow sensor and removal of the flow sensor.
 3. Theexhalation valve assembly of claim 2, wherein the condensate trapincludes a trap inlet port that directs the gas delivered to theexhalation valve assembly along an interior surface of a wall thatdefines the condensate chamber and wherein when assembled the wall thatdefines the condensate chamber of the condensate trap is exposed to theambient atmosphere.
 4. The exhalation valve assembly of claim 1, whereinthe valve body further includes at least one pressure sensor port. 5.The exhalation valve assembly of claim 4, wherein the valve body furtherincludes a first pressure sensor port between the inlet port and thevalve seat and a second pressure sensor port between the valve seat andthe exhaust port.
 6. The exhalation valve assembly of claim 1, whereinwhen assembled the actuator module is positioned vertically above thevalve module, the valve module is positioned vertically above the filtermodule and the filter module is positioned vertically above thecondensate trap.
 7. The exhalation valve assembly of claim 1, whereinthe seal element is removably connected to the removable valve body,such that when removed the valve chamber can be accessed for cleaning.8. The exhalation valve assembly of claim 1, wherein at least one coveris provided that creates a substantially trapped air space around thefilter body and flow sensor, the trapped air space insulating the filterbody and the flow sensor from the ambient atmosphere.
 9. The exhalationvalve assembly of claim 1, wherein the actuator module includes anactuator controlling displacement of a poppet that engages the sealelement of the valve module and engagement elements for removablyengaging the valve body.
 10. A respiratory ventilation systemcomprising: a pressure delivery system in a housing; an inspiratory limbthat receives respiratory gas from the pressure delivery system anddelivers the respiratory gas to a patient interface; an expiratory limbthat receives exhaled gas from the patient interface; a valve modulecomprising a valve body and attached seal element, the valve bodydefining an inlet port that receives the exhaled gas from the expiratorylimb and directs the exhaled gas through a valve seat to a valve chamberand an exhaust port allowing exhaled gas to exit the valve chamber, theinlet port and exhaust port being the only routes for gas to enter thevalve chamber, the valve seat opposite the attached seal element whereindisplacement of the seal element relative to the valve seat controls gaspressure within the expiratory limb; an actuator module removablyconnected to the valve module and, when attached to the valve module, isoperable to move the seal element relative to the valve seat to controlthe pressure of gas in the inlet port and the release of gas via theexhaust port; a filter module comprising a filter body containing filtermedia and wherein the filter module is removably and directlyconnectable to the valve module, wherein the filter module, whenattached to the valve module, filters gas delivered from the expiratorylimb prior to the gas entering the inlet port of the valve module; and aflow sensor contained in the valve body monitoring the flow of gasbetween the valve inlet port and the valve seat.
 11. The respiratoryventilation system of claim 10, wherein a portion of the valve body ismoveable to provide access to the flow sensor and removal of the flowsensor.
 12. The respiratory ventilation system of claim 10, wherein thevalve body further includes at least one pressure sensor port.
 13. Therespiratory ventilation system of claim 10 further comprising: acondensate trap including a trap body attached to the filter body, thecondensate trap receiving the gas delivered to the exhalation valveassembly prior to delivery of the gas to the filter body, wherein thecondensate trap holds the gas received in a condensate chamber for afirst residence time based on the condensate chamber's volume and gasflow therethrough and collects moisture that condenses from the gasduring the first residence time.
 14. The respiratory ventilation systemof claim 13, wherein the condensate trap includes a trap inlet port thatdirects the gas delivered to the exhalation valve assembly along aninterior surface of a wall that defines the condensate chamber andwherein the wall that defines the condensate chamber of the condensatetrap is exterior to the housing and exposed to the ambient atmosphereexternal to the pressure delivery system.
 15. The respiratoryventilation system of claim 13, wherein when assembled the actuatormodule is positioned vertically above the valve module, the valve moduleis positioned vertically above the filter module and the filter moduleis positioned vertically above the condensate trap.
 16. The respiratoryventilation system of claim 10 further comprising: a cover that wheninstalled on the respiratory ventilation system creates a substantiallyenclosed volume of trapped air within the housing and the at least onecover and around the filter chamber.
 17. A method of controllingpressure in an expiratory limb of a ventilation system comprising:receiving a patient's exhaled gas from an expiratory limb through afilter inlet port into a filter module comprising a filter bodycontaining filter media and wherein the filter module is removably anddirectly connectable to a valve module; filtering the exhaled gas byallowing a pressure differential between the expiratory limb and theatmosphere to drive the gas through the filter; passing the filteredexhaled gas into a removable valve body connected to the ventilationsystem, the removable valve body having a valve body inlet port, anexhalation port through which gas is released to the environment and asurface comprising a seal element, wherein the inlet port and exhaustport are the only routes for gas to enter the valve chamber; displacinga member external to the removable valve body that interfaces with theseal element on the removable valve body, thereby changing a distancebetween the seal element and a valve seat in the removable valve bodyand controlling the pressure of the exhaled gas in the expiratory limb;and monitoring the flow of gas with a flow meter located between thevalve inlet port and the valve seat of the removable valve body.
 18. Themethod of claim 17 further comprising: monitoring a difference inpressure between the exhaled gas in the ventilation system on theexpiratory limb-side of the valve seat and a gas pressure of theenvironment.
 19. The method of claim 18 further comprising: calculatinga first flow measurement from the difference in pressure and thedistance between the seal element and the valve seat; and performing anaction related to the delivery of gas to the patient based on acomparison of the first flow measurement and the monitored flow of gasfrom the flow meter.
 20. The method of claim 18 wherein performing anaction comprises one or more of indicating an alarm condition, changinga pressure of gas delivered to the patient based on the comparison ofthe first flow measurement and the monitored flow of gas from the flowmeter, and changing a flow of gas delivered to the patient based on thecomparison of the first flow measurement and the monitored flow of gasfrom the flow meter.